1. Field of the Invention
The field of the present invention is general aviation and, more particularly, the class of aircraft capable of vertical takeoff and landing (VTOL). The present invention further belongs to that subclass of VTOL aircraft with generally radial symmetry, designed for relatively low speed flight at low altitudes, suitable for use as an airport-to-downtown shuttle, home-to-office commuter, etc.
2. Related Art
The most common and widely employed vertical takeoff and landing (VTOL) aircraft is the helicopter. The success of this vehicle is due to the urgent need for this VTOL capability rather than to any particular distinction inherent in the genus. A short list of undesirable characteristics of helicopters include: long rotating blades which are a hazard to personnel and to the aircraft itself should they strike anything in the area, requirement for a remotely mounted propeller to counteract torque reaction of the airframe to the drive of the main rotor, complicated and relatively fragile rotor blade attack-angle controls, high maintenance requirements and rotor blades which must be long, thin, and relatively light and thus are flexible and subject to fatigue problems. Add to this incomplete list the fact that failure of any one of these components is likely to have catastrophic consequences for the aircraft and all on board and it is evident that an alternative design is desirable.
Man first flew in hot air balloons which, of course, are VTOL. The quest for heavier-than-air vehicles with this capability is approximately as old as any segment of the aircraft industry, but has accelerated since the end of World War II, and especially after the Vietnam War following the major role of helicopters in the latter conflict. A number of patents in the field of generally radially symmetrical aircraft have been granted, but it is not known that any have become successful in the market.
This may be due to the fact that these designs, while including many worthwhile ideas, did not integrate enough of them in any single concept, along with proven aircraft technology, to produce a practical product.
A significant problem which must be overcome in any VTOL aircraft is generation of sufficient "lift" to raise the vehicle off the ground.
A second problem is instability. Without the unidirectional airflow that exists across wings and tail surfaces under takeoff conditions in conventional aircraft, directional and stability problems become important. In the present invention gyroscopic effects of the large rotating fan increase stability and reduce said problems to a level well within the scope of pilot control.
Generation of a portion of the required lift is based on Bernoulli's Theorem which states that the energy of a fluid (such as air) is present in three separate energy forms; potential, pressure, and velocity, any one of which may be converted into any other.
In an airfoil section, the shape of said airfoil forces air flowing over the top to take a longer path than that of air flowing below said airfoil so that the air is forced to speed up, increasing its velocity energy. Since under these conditions, potential energy is relatively unaffected, the energy increase due to increase in speed is matched by a pressure decrease in said air.
Aircraft generally utilize this principle by incorporating an airfoil structure or "wing" which will produce this lowered air pressure on its upper surface when moved through the air. Air flowing under said wing is more or less unaffected, so that said average pressure decrease above said wing multiplied by the area of said wing appears as a net lifting force.
A second form of lift is generated by acceleration of a mass of air by a fan, propeller, wing, or other system. When a mass of air is changed from rest to a given velocity in a downward direction, an upwardly directed reaction force proportional to the mass times the velocity change, is produced. The more vertically the air is directed, the more effective this force becomes in producing lift.
A third means of producing lift when close to the ground, effective in takeoff and landing, is "Ground Effect." This is roughly equivalent to creating a zone of very slight compression in the air between the vehicle and the ground and using that pressure times the bottom area of the vehicle to help support said vehicle. This effect becomes stronger as the ground is approached and becomes negligible as the vehicle lifts away from the ground.
The present invention comprises a rational assembly of appropriate technology combined with integrated control systems to produce a practical aircraft. It is an object of the invention to provide a VTOL aircraft which is low in maintenance and relatively safe and simple to operate. It is an object of the invention to provide a VTOL aircraft that has performance characteristics similar to helicopters but without the shortcomings of a helicopter.